The present invention pertains generally to cluster tools. More particularly, the present invention pertains to cluster tools having a cathode for coating flat substrates with an extremely thin layer of metal particles. The present invention is particularly, but not exclusively, useful as a cluster tool having a cathode with an array of openings, for achieving a uniform directional deposition of metal particles in order to fill high aspect ratio or extremely narrow trenches on a substrate.
Cluster tools are well known in the prior art for placement of an extremely thin film of metal on a flat substrate, such as a wafer. To do this, an electrodeposition or a physical vapor deposition process is used wherein a sputtering cathode deposits metal particles on the substrate in a manner known in the art. These processes are also used for the filling of xe2x80x9ctrenchesxe2x80x9d that are formed in the substrate surface.
Usually, because of the extremely high voltages involved in the electrodeposition process, it is desired to use the physical vapor deposition process to coat a wafer with metal. This is feasible in cases where the trench width is not too small (approximately 1.0 xcexcm), or where the aspect ratio (ratio of desired depth to width of the trench) is not too high. However, it is often desired to fill 0.1 xcexcm wide trenches on a wafer, as well as high aspect ratio (very deep) trenches. Currently, filling such a trench with a metal layer such as Cu is problematic and requires using an electrodeposition method. What is desired is a PVD method that allows for filling of high aspect ratio trenches and trenches as narrow as 0.1 xcexcm wide.
It is known in the prior art the PVD processes use a magnetic field as a catalyst to cause the sputtering process to take place. Further, to fill a high aspect ratio trench, prior art devices have attempted to manipulate the magnetic field by increasing the intensity of the magnetic field. This increases the amount of metal particles which hit the flat substrate, which theoretically would increase the likelihood that high aspect or narrow trenches would become filled with metal particles. In practice, however, the high intensity magnetic field causes sputtered metal particles to impinge the substrate surface at an angle, which further tends to block the entrance to the trench and prevents any substantive filling of the trench. It would be much more effective to devise a device which would cause sputtering of the cathode target so that the particles of the cathode target impinge the substrate at an angle normal to the substrate surface.
U.S. Pat. No. 5,482,611, which issued, which issued to Helmer for an invention entitled xe2x80x9cPhysical Vapor Deposition Employing Ion Extraction From A Plasmaxe2x80x9d, describes a hollow cathode magnetron for producing intense plasma in a cathode container which ionizes a substantial percentage of sputter cathode (target) material. In Helmer, however, the magnetic trap is formed within the cathode container, which further effectively traps energetic electrons in a closed-loop magnetic tunnel with electrostatically reflective sidewalls. This requires a magnetron-assisted hollow cathode structure; otherwise, an undesirably high voltage will be required to operate the cathode.
In light of the above, it is an object of the present invention to provide a cluster tool with a sputtering cathode which can fill extremely narrow and high aspect ratio trenches on a flat substrate. It is another object of the present invention to provide a sputtering cathode which uses a PVD process to fill narrow manufacturing nodes and high aspect ratio trenches without the requirement of an initial seed layer. Yet another object of the present invention is to provide a sputtering cathode which can fill manufacturing nodes and high aspect ratio trenches without requiring an electrodeposition process. Another object of the present invention is to provide a sputtering target for a cluster tool which creates the effect of an array of hollow cathodes to achieve intense, yet uniform plasma without requiring an increase in the intensity of the magnetic field surrounding the cathode. It is another object of the present invention to provide a sputtering cathode for a cluster which is easy to manufacture and which can be used in a cost-efficient manner.
A cluster tool with a hollow cathode array in accordance with the present invention includes a base, a target and a source of magnetic flux lines. The base is formed with a recess, and the target is preferably disc-shaped with a substrate face and a base face and is shaped to interfit with the recess. The target is placed within the base recess so that the substrate face is oriented towards a spaced-apart flat substrate (usually a wafer), while the opposite face is in thermal contact with the base. Since the base is actively cooled via internal cooling lines, this allows heat removal from the target during operation of the cathode.
The base is formed with an inert gas feedhole, and the target is formed with a plurality of gas communication paths which extend through the target from the substrate face to the base face. The gas communication paths allow for inert gas to pass through the target during operation of the device.
To further distribute the inert gas more equally, the target can be subdivided into a top plate and a bottom plate. The top plate is formed with a plurality of through holes which extend through the plate. The bottom plate is formed with a plurality of distribution grooves on one side and with base face channels on the side which define the base face of the target. The bottom plate further includes a plurality of bottom plate openings which interconnect the base face channels in fluid communication with the distribution grooves (Alternatively, the bottom plate can be notched around the periphery thereof to connect the base face channels with the distribution grooves). When the top plate is placed on the bottom plate to establish the target, the through holes of the top plate combine with the distribution grooves, bottom plate openings and base face channels to establish the gas communication paths through the overall target. The above arrangement of the top plate and bottom plate allows for more even distribution of the inert gas through the target during operation of the device of the present invention.
The geometry of through holes in the top is selectively determined. More specifically, the maximum height of the through holes (which is equal to the thickness of the top plate) must be at least twice that of the maximum width of the through holes. Also, the through holes are preferably oriented normal to the substrate face of the top plate, but the through holes can be oriented so that they form an angle of up to forth-five degrees with the substrate face.
The magnetic source is preferably mounted to the underside of the base to ensure that the magnetic flux lines pass through the device of the present invention normal to the target. The magnetic flux lines passing through the target are parallel with the axes defined by each respect through hole. With this configuration, the magnetic lines of flux xe2x80x9cguidexe2x80x9d material that is sputtered from the through holes out of the through holes and causes the sputtered material to impinge on the substrate normal to the substrate. This further allows for more effectively of narrow width trenches during a deposition process.